[ms] Add support for parsing uuid as a Microsoft attribute.

Some Windows SDK classes, for example
Windows::Storage::Streams::IBufferByteAccess, use the ATL way of spelling
attributes:

  [uuid("....")] class IBufferByteAccess {};

To be able to use __uuidof() to grab the uuid off these types, clang needs to
support uuid as a Microsoft attribute. There was already code to skip Microsoft
attributes, extend that to look for uuid and parse it.  Use the new "Microsoft"
attribute type added in r280575 (and r280574, r280576) for this.

Final part of https://reviews.llvm.org/D23895

llvm-svn: 280578